The present invention relates to a process for coating a conveyed long, flexible support (hereinafter referred to as "a web" when applicable) with a liquid-type coating compound.
An example of a coating apparatus which has been extensively employed to coat a liquid-type coating compound (hereinafter referred to as "a coating liquid" when applicable) onto a web is the multi-layer slide bead coating apparatus described in U.S. Pat. No. 2,761,791, Russell et al. In this apparatus a plurality of coating liquids flow down the slide surface, and, at the lower end, strike against a conveyed web so as to form a bead, from which the coating liquids are applied to the web. Accordingly, in this coating apparatus it is essential to maintain the bead stable in order to successfully apply the coating liquids to the web. However, as the coating speed is increased, it becomes more difficult to maintain the bead stable.
In order to overcome this difficulty, an improved coating apparatus was proposed by Jackson in U.S. Pat. No. 3,928,678. This coating apparatus can eliminate the instability of the bead which results as the coating speed is increased. In the conventional coating apparatus, a lip-shaped member is provided at the lower edge of the slide surface for decreasing the speed of the layer of coating liquid flowing down the slide surface in order to increase the thickness of the liquid flow and to thereby stabilize the bead. With such a coating apparatus, particle effect in the coating liquid (appearance of stripes due to irregular coating) is observed, which may be attributed to an increase in the thickness of the layer of coating liquid. However, if one desires to increase the coating speed while the bead is maintained stable, this coating apparatus is unsuitable because the permissible increase in coating speed is not more than about 10%. Even that increase is possible only where the flow rate of coating liquid is relatively high. If the flow rate is relatively low, the permissible increase is sometimes lower than that of the Russell et al coating apparatus.
An object of this invention is to provide a coating apparatus in which all of the above-described difficulties accompanying a conventional coating apparatus have been eliminated and the coating speed can be greatly increased, especially in the case where the flow rate of coating liquid is relatively low. In particular, it is directed to the reduction of coating defects associated with a standing wave in the coating of a silver halide emulsion upon a support.